The present invention relates to a filter device, especially for filtering melt-like fluids, such as polymer melts, having at least one filter disk made up of two filter disk halves. The filter disk halves are connected with one another along one edge and are fitted with a fabric or cloth fabric filter material aligned on the exterior. The disk halves are held at some distance from one another by a support arrangement to define a hollow space between them having an essentially open flow-through passage. In the interior, an outlet opening is provided for the melt-like fluid.
U.S. Pat. No. 4,902,420 discloses a filter arrangement with a multi-layer construction. Between the fabric or cloth fabric filter materials lying facing one another a drainage plate is inserted as support device Longitudinal slots extend from the exterior to the interior to define a hollow space of small volume between the fabric or cloth fabric filter materials. The medium to be filtered, for example a polymer melt, in this system is subjected to increased flow resistance, so that the filter capacity is correspondingly decreased. Because of the complicated construction and the multiplicity of parts, the manufacturing costs are higher. Furthermore, the separation of the fluid streams in the filter disk occurring by the separation into various longitudinal slots causes the so-called memory effect. If, for instance, there is subsequent formation of blowholes or such phenomena out of the polymer melts, this leads to undesired formations of strips or lamina.
DE-AS 1,096,331 discloses a filter device having at least one filter disk formed of two filter disk halves connected with one another. Between them, the filter disk halves limit an essentially open passage, allowing flow-through in the hollow space. A fabric or cloth fabric filter material is aligned on the disk halves exterior. The filter disk half has a metal disk with discharge openings or is constructed of spoke-like fillets. Coiled ribs or fins or fillets are used as a support arrangement, and extend radially inward and at some distance from one another over the entire hollow space, which tapers conically outward to the exterior periphery. Insufficient support is provided for the filter disk halves with their fabric or cloth filter material, so that this filter arrangement can be used only in a limited manner. Especially when high pressures are present, it cannot be used without danger of breakdown. Additionally, the ribs or fins used in this filter arrangement separate the hollow space which is preferably open to flow-through into individual chambers. Here too, the flow resistance is increased, so that this filter arrangement does not suffice for the filtering of melt-like fluids.
Objects of the present invention are to provide improved filter arrangements which can be manufactured at low cost and which allow an increased filtering capacity during operation. Especially for the filtering of melt-like fluids, such as polymer melts, it can be designed for use under high pressures.
The support arrangement includes individual supporting cams with essentially identical exterior dimensions. The cams extend outwardly from the discharge opening, are arranged in a plurality of groups, are separated from one another radially, are securely connected with at least one of the two filter disk halves and pass through the hollow space. In this manner, each filter disk half is in contact with the other filter disk half, and the entire hollow space is available as an essentially open flow-through passage. The above-described drainage plates can then be deleted to save cost. Consequently, the flow volume of the melt-like fluid to be filtered, such as polymer melts, and consequently also the filtering capacity, are increased.
As a result of having the plurality of supporting cams arranged in groups, extending between the two filter disk halves of a filter disk and supporting this disk assembly, a high resistance to pressure stresses on the filter disk halves as well as on their fabric or cloth fabric filter materials is attained. Overall, a highly pressure-stable filter disk is realized for use in the filter device. Simultaneously, the offset arrangement of the supporting cams causes mixing of the melt flow, which thus counters the memory-effect.
With one preferred embodiment of the filter device according to the present invention, the individual group arrangements of supporting cams are arranged at different radial distances from the outlet opening and are aligned along concentric circles around this outlet opening. Such an arrangement allows a high degree of support for the filter disk halves. Accordingly, such arrangement has only a slightly negative influence on the dimensions of the opening of the, hollow space for flow-through between the filter disk halves in the sense of causing only a slight increase of flow resistance. Also, a favorable means of manufacturing the filter disk, and consequently the entire filter device, can be attained in this manner.
In another preferred embodiment of the filter device according to the present invention, the two filter disk halves of a filter disk are provided with supporting cams of identical dimensions on the adjacent and facing sides. Such sides either engage along a longitudinal separation line of the filter disk halves where they abut one another, and/or, wit contact with the relevant other filter disk half, they engage in the free spaces between the supporting cams of each relevant facing filter disk half. With such described arrangements, to save on outlay, the filter disk can be composed of identically constructed filter disk halves.
The outlay for the manufacture can be further decreased, insofar as the supporting cams are connected tightly with the relevant filter disk halves, by means of weld points produced by a projection-weld method.
With another preferred embodiment of the filter device according to the present invention, the two filter disk halves extend parallel to one another and define a disk-shaped hollow space of identical dimensions. A favorable flow-through of the melt-like fluid is attained in this manner, without increasing the wall shearing or thrust stresses when it comes to the flow resistance with the flow of the melt though the filter disk.
With one especially preferred embodiment of the filter device according to the present invention, the supporting cams form fillet-like solid box profiles. Such cams, in turn, can be mounted on the filter disk halves in such a manner that they free the discharge openings in the filter disk halves. As a result of the use of the solid box section profiles, the fabric or cloth fabric filter materials on the outside of the two filter disk halves of a filter disk can be securely supported and are not drawn into the box section profile of the supporting cams. For example, the filter materials could be drawn into the box section profile, if the supporting cams would be shaped out of the filter disk halves by a deepdrawing method or the like. Since the box section profiles are embodied as fillet-like, they can be used beneficially in the intermediate spaces between the openings of a filter disk half. They then do not have the capacity to negatively influence the open flow-through through these discharge openings. The arrangement can especially avoid the generation of flow shadows, since the discharge openings are grouped without any side spacing directly around the supporting cams and are left free.
With another especially preferred embodiment of the filter device according to the present invention, the discharge openings are formed in the filter disk halves by means of circular cutouts. In groups of different magnitudes, the circular cutouts extend along concentric circles around the outlet opening. By a certain selection of the grouping with discharge openings in the form of rows of holes, the flow ratios within the filter disk can improve for the melt-like fluid, and thus, the filter capacity can be increased. Preferably the filter disk halves and the supporting cams are formed of top-grade steel, so that these are not inclined to corrode, and consequently, cannot pollute the melt-like fluid. Insofar as spacing cams are arranged on the top and bottom of the filter disk, especially in the peripheral side border areas where the filter disk halves are connected with one another by a border welding joint, then in a cost-saving manner the traditional so-called spacer can be deleted. The known filter device would then serve to hold the filter disks inside the assembly at some spacing from one another Such a spacing is now realized by means of the spacing cams arranged directly on the filter disks.
Other objects, advantages and salient features of the present invention will become apparent from the following detailed description, which, taken in conjunction with the annexed drawings, discloses preferred embodiments of the present invention.